U.S. patent number 4,653,862 [Application Number 06/818,470] was granted by the patent office on 1987-03-31 for liquid crystal display device having color filters sized to prevent light leakage between pixels.
This patent grant is currently assigned to Seiko Epson Corporation. Invention is credited to Shinji Morozumi.
United States Patent |
4,653,862 |
Morozumi |
March 31, 1987 |
Liquid crystal display device having color filters sized to prevent
light leakage between pixels
Abstract
A multi-color liquid crystal display includes liquid crystal
micro-shutters which open and close color filters arranged as dots
in a mosaic or stripe pattern. Fine and clear color image display
and color graphic display are realized in the device wherein the
filters are within the LCD panel, being formed on one substrate and
covered by the driving electrode.
Inventors: |
Morozumi; Shinji (Suwa,
JP) |
Assignee: |
Seiko Epson Corporation (Tokyo,
JP)
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Family
ID: |
15961914 |
Appl.
No.: |
06/818,470 |
Filed: |
January 13, 1986 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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472358 |
Mar 4, 1983 |
4600274 |
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Foreign Application Priority Data
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Oct 1, 1982 [JP] |
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57-173513 |
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Current U.S.
Class: |
349/109; 349/110;
349/138; 349/145 |
Current CPC
Class: |
G09G
3/3607 (20130101); G02F 1/133514 (20130101) |
Current International
Class: |
G02F
1/13 (20060101); G02F 1/1335 (20060101); G09G
3/36 (20060101); G02F 001/13 () |
Field of
Search: |
;350/333,339R,339F |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0023421 |
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Feb 1981 |
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EP |
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0022898 |
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Feb 1977 |
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JP |
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0025174 |
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Mar 1981 |
|
JP |
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0186737 |
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Nov 1982 |
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JP |
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Primary Examiner: Corbin; John K.
Assistant Examiner: Gallivan; Richard F.
Attorney, Agent or Firm: Blum Kaplan Friedman Silberman
& Beran
Parent Case Text
This is a division, of application Ser. No. 06/472,358 filed Mar.
4, 1983, now U.S. Pat. No. 4,600,274.
Claims
What is claimed is:
1. A liquid crystal display device having a plurality of picture
elements arranged in a matrix of columns and rows, each of said
picture elements comprising:
a first substrate and a second substrate, said substrates facing
each other and spaced apart for defining a space therebetween;
a first electrode formed on the surface of said first substrate
facing said second substrate;
a color filter and a second electrode formed on the surface of said
second substrate facing said first electrode and said first
substrate;
each color filter on the second substrate having an area greater
than the area of the first electrode on the first substrate with
the second electrode formed on the surface of the color filter;
and
a liquid crystal material filling the space between said electrodes
and retained in said space.
2. A liquid crystal display device as claimed in claim 1, further
including a data line and intermediate component means for
connecting the data line to said first electrode through the
intermediate component means, said intermediate component means
being one of a thin film transistor and non-linear elements, said
intermediate component being formed on said first substrate on the
same surface with said first electrode.
3. A liquid crystal display device as claimed in claim 2, wherein
said non-linear element is one of diodes connected oppositely and a
MIM element.
4. A liquid crystal display device as claimed in claim 2, wherein
all said color filters are formed on the same second substrate, and
all said first electrodes are formed on the same said first
substrate.
5. A liquid crystal display device as claimed in claim 2, wherein
said electrodes are transparent.
6. A liquid crystal display device as claimed in claim 2, wherein
said color filters represent three primary colors, each said first
electrode having a shape similar to that of the opposed color
filter.
7. A liquid crystal display device as claimed in claim 6, wherein
said primary color filters are arranged in said matrix in a pattern
of one of stripes of a first color adjacent to stripes of two other
colors and a mosaic of colors.
8. A liquid crystal display device as claimed in claim 7, wherein
said pattern is a mosaic, the centers of the picture elements in
one row being shifted by a selected distance from the centers of
the picture elements in the next adjacent row.
9. A liquid crystal display device as claimed in claim 8, wherein
said selected distance is 1/2 of the distance between centers of
adjacent elements in the same row.
10. A liquid crystal display device as claimed in claim 7, wherein
said pattern is a mosaic, the centers of picture elements in a
column being shifted by a selected difference from the centers of
picture elements in the next adjacent column.
11. A liquid crystal display device as claimed in claim 10, wherein
said selected distance is 1/2 of the distance between centers of
adjacent elements in the same column.
12. A liquid crystal display device as claimed in claim 1, wherein
said color filters represent three primary colors, each said first
driving electrode having a shape similar to that of the opposed
color filter.
13. A liquid crystal display device as claimed in claim 12, and
further comprising a passivation layer formed on said color filters
between said color filters and said second driving electrode, said
passivation layer preventing interaction between said filters and
said electrode materials.
14. A liquid crystal display device as claimed in claim 13, wherein
said first and second substrates are glass, and said passivation
layer is SiO2.
15. A liquid crystal display device as claimed in claim 1, wherein
said color filters are formed of a water soluble organic resin
colored with a coloring material.
16. A liquid crystal display device as claimed in claim 15, wherein
said organic resin is one of polyvinyl alcohol and gelatine.
17. A liquid crystal display device as claimed in claim 1, wherein
a layer of glass separates said color filters from said second
electrode.
18. A liquid crystal display device as claimed in claim 1, wherein
said color filters represent three primary colors and white, said
picture element being arranged in blocks of four including said
primary colors and white.
19. A liquid crystal display device as claimed in claim 1, wherein
said first and second substrates are transparent.
20. A liquid crystal display device as claimed in claim 1, wherein
said color filter is formed directly on the surface of said second
substrate and said second electrode covers said color filter.
21. A liquid crystal display device as claimed in claim 1, wherein
said second driving electrode is disposed directly on adjacent to
said second substrate and said color filter covers said second
driving electrode.
22. The liquid crystal display device of claim 1, wherein the
second electrode is a portion of a common electrode of the device
which covers a plurality of the color filters of the picture
elements of the matrix.
23. A liquid crystal display device having a plurality of picture
elements arranged in a matrix of columns and rows, each of the
picture elements comprising:
a first substrate and an opposed spaced apart second substrate for
defining a space therebetween;
a first electrode on the surface of the first substrate facing the
second substrate;
a color filter and a second electrode on the surface of the second
substrate facing the first electrode and the first substrate;
a liquid crystal material filling the space between the electrodes
and retained in the space; and
means for reducing the leakage of incident light in the regions
between the first electrodes of adjacent picture elements of the
matrix.
24. The liquid crystal display device of claim 23, wherein the
means for reducing the leakage of incident light includes a color
filter on the second substrate having an area greater than the area
of the first electrode on the first substrate.
25. The liquid crystal display device of claim 23, wherein the
means for reducing the leakage of incident light includes a black
frame between picture elements of the matrix.
26. The liquid display device of claim 25, wherein the black frame
is a black pigment disposed between adjacent color filters of the
matrix.
27. The liquid crystal display device of claim 25, wherein the
black frame is a black pigment disposed between adjacent first
electrodes of the matrix.
28. The liquid crystal display device of claim 25, further
including a plurality of parallel and spaced apart data lines on
the first substrate adjacent to the first electrodes, polarizers
disposed on the outer surfaces of the substrates with the axes of
polarization substantially perpendicular to each other and circuit
means including means for applying a voltage to the liquid crystal
material and the means for reducing leakage of incident light
includes means for continually applying a video signal to the data
lines so that the data lines appear black to a viewer.
Description
BACKGROUND OF THE INVENTION
This invention relates to a liquid crystal display device and more
particularly to a liquid crystal display for colored picture images
and color graphics. Heretofore, it has not been possible to realize
a practical liquid crystal display device with a multi-color
display for the following reasons. First, the prior art was not
capable of enlarging the number of dots or lines in the liquid
crystal panel. These devices were limited at most to a 1/16 duty
cycle ratio and thus, sixteen lines in a conventional multiplex
driving system. On the other hand, a color display system requires
at least a hundred lines and accordingly, 1/100 duty cycle ratio
must be achieved for driving a color liquid crystal device.
Second, it has not been possible to have a superior medium for
multi-colored display in using a liquid crystal device. For
example, it is extremely difficult to achieve a multi-color display
using only one substrate when coloring materials are included in
the liquid as in guest-host liquid crystals. Also, it is very
expensive to superimpose panels having different color compositions
and such a multi-panel construction cannot realize a fine quality
color display. Also, viewing angle is extremely limited if a color
filter is used outside the liquid crystal panel.
For these reasons it has been difficult to produce a practical
liquid crystal panel with a multi-color display.
What is needed is a multi-color liquid crystal display which is
economical to produce and provides high quality color picture
images and graphics.
SUMMARY OF THE INVENTION
Generally speaking, in accordance with the invention, a liquid
crystal display especially suitable for providing images and
graphics in multi-color is provided. Three systems for increasing
the duty cycle ratio are disclosed. A very high duty cycle ratio,
in the order of 1/60 to 1/200 is achieved in a multiplex driving
system as a result of and using exceptional construction techniques
for the liquid crystal panel. The liquid crystal electrodes are
switched by means of active matrix elements such as transistor
switches, and non-linear elements such as a diode or MIM element.
The multi-color liquid crystal display in accordance with the
invention includes negative liquid crystal micro-shutters which
open and close color filter dots arranged in a mosaic or stripe
pattern as the technique for producing a superior color display
device. The filter is within the display panel. Fine and clear
color image display and color graphic display are realized in the
liquid crystal display device in accordance with the invention.
Accordingly, it is an object of this invention to provide an
improved liquid crystal display device of simple construction
capable of producing color images and graphics of high quality.
Another object of this invention is to provide an improved color
liquid crystal display device which has good resolving power and
clearness.
A further object of this invention is to provide an improved liquid
crystal display which operates with a very high duty cycle ratio
and allows for a display of at least a hundred lines.
Still other objects and advantages of the invention will in part be
obvious and will in part be apparent from the specification.
The invention accordingly comprises the features of construction,
combination of elements, and arrangement of parts which will be
exemplified in the constructions hereinafter set forth, and the
scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
For a fuller understanding of the invention, reference is had to
the following description taken in connection with the accompanying
drawings, in which:
FIG. 1 is a cross-sectional view of a liquid crystal display device
in accordance with the invention;
FIGS. 2 and 3 show details in construction of a color filter used
in the liquid crystal display device of FIG. 1;
FIGS. 4a, c are top and side sectional views of an active matrix
base substrate in accordance with the invention; and
FIG. 4b is an equivalent circuit thereof;
FIG. 5a, b are top and side sectional views of a non-linear element
for use in a liquid crystal display device in accordance with the
invention;
FIGS. 6a, b are top and side sectional views of a non-linear
element for use in a liquid crystal display device in accordance
with the invention;
FIG. 7 shows the voltage-current characteristics of a nonlinear
element;
FIG. 8 is an equivalent driving circuit;
FIGS. 9a-c show the construction of a color display device similar
to FIG. 1 in accordance with the invention;
FIGS. 10, 11, 12, 16 and 18 illustrate functional circuit
arrangements and driving methods for color filters for use in a
liquid crystal display device in accordance with the invention;
FIG. 13 illustrates operating waveforms associated with the
functional circuit of FIG. 12;
FIG. 14 is a circuit for generating clock signals associated with
the circuit of FIG. 12;
FIG. 15 illustrates waveforms associated with the circuit of FIG.
14; and
FIG. 19 illustrates waveforms associated with the circuit of FIG.
18;
FIGS. 17a, b illustrate the contrast characteristics of a liquid
crystal in relation to the applied voltage and a sample-hold
operation performed on a video signal;
FIGS. 20a, b, illustrate fundamental constructions of high
resolving power picture elements in accordance with the
invention;
FIG. 21 is the construction of a driving electrode in a multiplex
driving system in accordance with the invention;
FIG. 22a, b, FIG. 23, FIG. 24 and FIG. 25 illustrate the use of a
thin-filmed transistor in a high resolution picture element
construction in accordance with the invention; and
FIG. 26 illustrates a high resolving power picture element using a
non-linear element in a construction in accordance with the
invention.
FIG. 27 is a view similar to FIG. 9a of an alternative embodiment
of a liquid crystal display device in accordance with the
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a basic structure of a liquid crystal display
device in accordance with the invention. Three different types of
color filters are formed on a glass substrate 1, for example, red
filter 8, green filter 9 and blue filter 10 are formed as a mosaic
or stripe pattern. A passivation layer 6, for example, SiO2, is
formed on these color filters, and a transparent electrode 5,
serving as a liquid crystal driving electrode is formed on the
passivation layer 6. There is also a construction where the
passivation layer 6 can be omitted as described hereinafter.
Opposed to the electrode 5 is a device layer 3 on which switching
elements or non-linear elements are arranged. The device layer 3 is
formed on a glass substrate 2 and transparent electrodes 4 are
formed on the device layer 3 in correspondence with every color
filter dot 8, 9, 10 for driving the liquid crystal.
With both of the above described glass substrates 1, 2 positioned
in opposition, a liquid crystal material 7 is encapsulated in the
space between the glass substrate 1 and the glass substrate 2 by
sealing around the periphery of the glass substrates.
In a transparent type of display panel, light is introduced from
beneath the glass substrate 1 through a polarizer. Light having a
fixed wavelength corresponding to a predetermined color is
transmitted through color filters 8, 9 and 10 by opening the
transparent electrode 4. Light is not transmitted at a dark portion
of the liquid crystal wherein voltage is not supplied to the
electrode 4 of the liquid crystal. Light having a wavelength
corresponding to the color filter is transmitted only at the
transparent portions of the liquid crystal wherein voltage is
supplied to the electrodes of the three primary colors to yield
seven colors for graphic display. Further, various degrees of
luminance levels of full colors are realized by adopting a gray
scale display function which controls semi-transparent states of
the liquid crystal 7.
Further details of the construction of FIG. 1 follow. FIG. 2 shows
a structural example of a color filter. A water soluble organic
resin layer, for example polyvinyl alcohol, gelatine, or the like,
is formed on a transparent glass substrate 20. Then, the water
soluble organic layer is colored with coloring materials of red,
blue and green by printing these coloring materials in an
arrangement having a predetermined pattern. As a result, each color
filter is formed so as to be arranged in correspondence to each
transparent electrode 4 (FIG. 1). In FIG. 2, the color filter
includes red portions 22, blue portions 23 and a green portion 24.
In addition, a black frame 21 is provided between the color filters
by coloring the boundary of each primary color with a black pigment
in order to avoid blurring of the color at the filter boundaries.
However, a black frame 21 is not required when the colored layer,
such as gelatine, and the like is etched off. In the case of a
negative type liquid crystal, an inhibitor of coloring must be
included in the black frame 21 instead of a black coloring material
when the coloring power of the coloring material is strong in the
lateral direction.
Next, a transparent passivation film 25 is formed on the color
filter and then a transparent conductive electrode 26 is formed on
the passivation film 25 for driving the liquid crystal. This
electrode 26 is photoetched to obtain the necessary pattern, thus,
a lower electrode portion is formed. There is a construction where
the transparent electrode 26 is formed directly onto the color film
without the passivation filter 25. In this construction, the
transparent film 26 also functions as a passivation film.
The coloring materials in the color filters 22, 23, 24 may be
deteriorated or damaged when the transparent conductance film 26 is
formed. This disadvantage is avoided by forming the passivation
layer. With reference to FIG. 3, this disadvantage can be avoided
by forming a passivation layer 34 on a color filter 31 or by
forming a transparent electrode 33 on a thin glass or plastic film
32 and then adhering the layered structure 32, 33 to the glass
substrate 30 having the filters 31 thereon.
FIG. 4 shows an embodiment of an active matrix element constructed
on a transparent substrate. This construction has an advantage in
that a driving duty cycle greater than 1:00 can be attained and a
gray scale display can be easily achieved in this system. FIG. 4
illustrates a silicon thin film transistor on a transparent
substrate, such as pyrex, quartz, and the like having a
comparatively high melting point. Thus, a thin film transistor is
more easily formed on a transparent substrate as compared to
forming conventional active matrix elements on a single crystal
wafer of silicon. A plan view in FIG. 4a illustrates a cell 41
which is one picture element, that is, one dot in a matrix. A gate
line 44 is connected to the gate of a transistor 49 to serve as a
selecting line Y, and a data line 43 is connected to the source of
the transistor 49 through a contact hole 47 to serve as an X line.
An electrode 42 for driving the liquid crystal is connected to the
drain of the transistor 49 through a contact hole 46. Also, a
capacitor 48 for storing an electrical charge is formed between a
ground line 45 and the electrode 42 for driving a liquid crystal
material.
The circuit in FIG. 4b is an electrical equivalent to the
construction of the cell 41 in FIG. 4a. When the transistor 49
turns ON, a voltage is applied through the data line 43 to the
capacitor 48 and the liquid crystal driving electrode 42. Then, an
electrical charge is stored by the capacitor between opposite
electrodes, of the capacitor 48 and the driving electrode 42. The
electrical charge can be kept for a long time because the current
leakage of the transistor 49 and the liquid crystal material is
negligibly small. Therefore, a principle duty cycle ratio can be
the time of electrical charge retention in the capacitor divided by
the time necessary for inputting a data signal. The value of the
duty cycle ratio with this construction can be greater than 10,000.
However, the capacitor 48 does not require a large area of the
liquid crystal driving electrode.
FIG. 4c is a sectional view taken along the line c--c of FIG. 4a. A
first thin film layer of a silicon channel region is formed on a
transparent substrate 40 by a process of low pressure chemical
vapor deposit (CVD), or plasma CVD, after a patterning treatment is
performed. An oxidized layer is formed by oxidizing the silicon
surface and then, a second film layer of silicon is formed. Then, a
gate line and ground line are formed by patterning a second thin
film layer of silicon. The oxidized layer is etched by utilizing
the second thin film as an etching mask. Thus, a gate insulating
film 51 and a gate electrode 50 are formed. A N-layer is formed by
implanting positive ions into the first layer of silicon by using
the gate 50 as a mask. Thus, the source 53, channel 55 and drain 54
of the transistor are constructed.
After the oxidized layer is deposited, a contact hole is formed and
then the data line 43 and liquid crystal electrode 42 are formed by
depositing transparent conductive film and patterning the thin
film. In this construction, the liquid crystal driving electrode
plays the role of a light shutter so that colored light coming from
the filter corresponding to the electrode position is transmitted
or cut off by the shutter.
Furthermore, a gray scale display is attained by varying light
transmittance of the liquid crystal material continuously by
controlling the level of input voltage of the data line. This
display has a great advantage in realizing full colors which are
formed by mixing of the primary three colors while keeping the gray
scale levels of the color itself. Another advantage is that a
complete color image composed of 500.times.500 dots in a matrix can
be achieved because such a system can operate with an extremely
high duty ratio when operating as a point-at-a-time system.
Another means for improving the driving duty cycle of a liquid
crystal display in accordance with the invention is to drive the
liquid crystal by utilizing a non-linear element such as
illustrated in FIGS. 5 and 6. FIG. 5 shows an exemplary
construction of a metal-insulator-metal (MIM) element wherein a
matrix cell 61 is comprised of a driving electrode 57, MIM element
62 and an X driving line or film 58. This driving electrode 57 is
driven by applying a data signal to the electrode 57 by way of the
MIM element 62 from the X driving line or film 58, the film 58 of
tantalum Ta, is formed by sputtering and then patterning the
tantalum film. Further, an oxidized layer of from 300 to 500
angstroms in thickness is formed on the tantalum film 58 anodizing
this film. After that, a tantalum layer 60 is formed by sputtering
and then patterning the tantalum film so as to be the upper
electrode. Then, a transparent driving electrode 57 is formed.
FIG. 6 is an exemplary construction wherein two diodes faced
oppositely to each other are connected in series and the X driving
line 66 is connected to an electrode 65 through a N type area 67, P
type area 68 and N type area 69. FIG. 6b is a sectional view along
the line b-b of FIG. 6a and the construction process is as follows.
After forming an island of a silicon layer on a transparent
substrate 63, N type areas 67, 69 and P type areas 68 are formed
through ion implantation. Further, a transparent conductive film is
formed and then an X driving line 66 and liquid crystal driving
electrode 65 are formed. It should be understood that a PNP
construction is also possible.
A non-linear element constructed by the above described methods
show voltage-current characteristics as indicated in FIG. 7 wherein
the current increases sharply at a certain level of input voltage.
FIG. 8 is an equivalent circuit showing a driving liquid crystal
cell 81 and this non-linear element 80. The non-linear element 80
is represented as a non-linear resistance RM and a capacitor CM.
The liquid crystal 81 is represented as an equivalent resistance RL
and a capacitor CL.
An operating voltage higher than a threshold level is applied to
the non-linear element 80 in order to light the liquid crystal when
the voltage VM between the crystal cell 81 and nonlinear element 80
is almost equal to the operating voltage VD because the resistor RM
is at a low value. Therefore, the voltage VM is substantially
applied to the liquid crystal. Thereafter, the resistance RM
becomes extremely high when the operating voltage VD is reduced
below the threshold level. Then, the voltage VM which is stored in
the capacitor CL gradually diminishes by discharging the capacitor
CL with a time constant determined by the values of RL and CL.
However, a voltage level which lights the liquid crystal can be
maintained for a long period of time.
When the liquid crystal is not lit, VM is nearly zero voltage
because a lower voltage than the threshold voltage is applied at
VD.
Therefore, the voltage VM for lighting the liquid crystal is
maintained by the capacitor CL, regardless of voltage level, so
that a duty cycle ratio can be increased, which is a similar result
as that of the active matrix shown in FIG. 4. In the constructions
of FIGS. 5 and 6, the driving electrodes 57, 65 play the role of a
light shutter aligned to the color filter.
The advantage of a non-linear element is its simple construction
when a simple multiplex driving method of the prior art is
available having a duty cycle ratio which is either 1/2 or 1/16.
The non-linear element is applicable to gray scale display as well
as to graphic display. There are two methods of driving a liquid
crystal for realizing gray scale display. One is where an active
matrix with thin film transistors (TFT) is adapted to a system
where continuous gray scale can be achieved by applying voltages
corresponding to the contrast level or gray scale to data line D in
FIG. 4. The voltages corresponding to the gray scale are obtained
by sampling and holding an image signal, that is, a point-at-a-time
system.
Another method of driving the liquid crystal for realizing gray
scale display is with multiplex driving at a high duty cycle ratio
by varying the pulse width of the driving signals. For instance
sixteen levels of gray scale can be obtained by dividing a
selecting frame into sixteen categories wherein each category means
one level of the gray scale. The above-mentioned pulse width
modulation system is a line-at-a-time system.
When another liquid crystal panel, in accordance with the
invention, that is, wherein a non-linear element is applied, both a
line-at-a-time driving system and a point-at-a-time driving system
are available for use as described more fully hereinafter.
In summary, in accordance with the invention, a switching element
or non-linear element is formed on a glass substrate which
constitutes the upper electrode for driving the liquid crystal.
Another glass substrate provided with a filter constitutes the
lower electrode for driving the liquid crystal. Direct formation of
the element on the filter shown in FIG. 2 deteriorates the filter
charcteristics and decreases the yield of the filter. There are two
ways of avoiding these difficulties, namely, that switching
elements are formed on a thin sheet 32 as shown in FIG. 3 and then
attached to the lower filter portion. Another way of avoiding these
difficulties is by forming the switching elements directly on the
glass substrate and the color filter layer is formed on these
switching elements.
FIG. 9 illustrates an example of a display panel in accordance with
the invention. This sectional view in FIG. 9a shows the upper
portion to be comprised of a glass substrate 99, switching element
portion 90 and driving electrodes 97. The lower portion of the
display is comprised of color filters 92, 93, 94 on a glass
substrate 91, and a common electrode 96 acting through a
passivation layer 95. A liquid crystal layer 98 is inserted between
the above described two glass substrates 90, 91 and a polarizing
plate is attached to either of the upper or lower portions. Light
is applied from an external source through the polarizing
plate.
In FIGS. 9a-c the common electrodes 96 are arranged as stripes in
the horizontal direction of the Figures. It should be understood
that in an alternative embodiment in accordance with the invention
the common electrode 96 is one element covering all of the picture
elements of a display.
Here there is a problem of light shielding because of gaps existing
between color filters or between driving electrodes where light
enters these gaps and deteriorates an otherwise beautiful color
reproduction. For instance, when light is irradiated from the lower
portion, this light leaks away from the gaps between color filters
and between driving electrodes even when the liquid crystal shutter
is closed.
There are two techniques to counter the above-mentioned problem.
One technique uses a negative-type liquid crystal material wherein
light cannot be transmitted without applying a voltage. Thereby, a
transmittance of light is always shielded through the gaps between
the driving electrodes 97. The other technique is to include dark
frames in the gaps between color filters as shown in FIG. 2. The
use of these counter measures together brings an even more
effective result.
Light can become blurred when passing through the liquid crystal
material at the time when the shutter is open. For instance, when
only a shutter above a red filter 92 is open, light at the edge of
the blue filter 94 and green filter 93 leaks from the shutter onto
the red filter 92 and the light leakage deteriorates the color
image reproduction. To avoid this problem a large area of color
filter is preferably adopted as compared with the area of the
effective shutter in the liquid crystal. For example, the driving
electrode 97 of an active matrix is formed smaller than the
mosaic-state filter as illustrated in FIG. 9b.
In FIG. 9c, a view looking through the transparent layers as
indicated by the arrow in FIG. 9a, a non-linear element is provided
wherein the overlapping portion of the lower common electrode 96
and the upper driving electrode 97 is the effective shutter
portion. This area is formed larger than the strip-type color
filter or mosaic-type color filter.
In the constructions of a liquid crystal display device in
accordance with the invention, described above, the common
electrode, for example, electrode 96 of FIG. 9a covers the color
filters 92, 93, 94. Because of the transparency of the filters 92,
93, 94, passivation layer 95 and common electrode 96, in an
alternative embodiment of a liquid crystal display device in
accordance with the invention, the relative positions of the color
filters and the common electrode may be reversed as illustrated in
FIG. 27. In FIG. 27, which is similar to FIG. 9a and uses the same
reference numerals to identify the same elements, the common
electrode 96 is adjacent to the glass substrate 91. The passivation
layer 95 and color filters 92, 93, 94 cover the common electrode 96
and separate the common electrode from the liquid crystal material
98. The upper portion of the device of FIG. 27 is identical with
that of FIG. 9a and the description relevant to FIG. 9c is equally
applicable to the construction of FIG. 27.
In the above display system for a color liquid crystal display
device in accordance with the invention, it is necessary that the
difference of light transmittance between an open stae of the
liquid crystal shutter and the closed state of the liquid crystal
shutter be large. With respect to a TN display device, which is
conventionally used, two polarizing plates are prepared. One is put
on the upper side and the other on the lower side of the display
panel and the polarizing plates are adjusted to be of the positive
type. In this case, the ratio of light transmittance of a shutter
is determined by the arrangement of polarizing light plates, and
the ratio of parallel direction of polarizing plates to the
vertical direction of these plates. As a practical matter, this
ratio ranges from 10 to 50.
When using guest-host liquid crystal material, the brightness is
twice that compared with TN liquid crystal material, and the
transmittance ratio is entirely determined by the liquid crystal
materials, and this ratio is relatively large because only one
polarizing plate is needed. For instance, generally a guesthost
liquid crystal including black coloring material completely cuts
off the light, and becomes very transparent when voltage is applied
so that the ratio of light transmittance is over 50.
Additionally, a positive-type of guest host liquid crystal shows
excellent characteristics compared to the negative type especially
when considering stability, reliability, lower driving voltage and
a large transmittance ratio, which is a very important factor in
this invention. Further, a positive type of guest-host liquid
crystal is favorable in avoiding leakage and blurring of light as
described above. Thus, this type of material is entirely suitable
for full color display in accordance with the invention and
particularly black coloring material gives excellent performance of
three primary colors reproduction.
FIG. 10 illustrates an exemplary filter arrangement and driving
method for a color liquid crystal display using a pointat-a-time
method in accordance with the invention. Filters 106 of three
primary colors (red R, blue B, green G,) are arranged as stripes
extended in a Y direction. Driving electrodes on the sides of the
filters are arranged as stripes or all over the surface in the same
Y direction as the filters 106. Upper electrodes 105 are arranged
in the X direction and divided into every picture element from Xl
to Xn. A shift register 101 outputs signals S1...Sn to the
transistors 104 in sequence in synchronism with a transmitting
clock signal .phi.5, and video signals VS are inputted to the
elements Xl through Xn successively by activating the associated
transistor 104. This is known as a point-at-a-time method.
The shift register 102 selects driving electrodes Yl through Ym
successively in synchronism with a clock signal .phi.4. For each Y
line which is selected, three color signals VSR, VSB, and VSG are
selected in synchronism with clock signals .phi.1 through .phi.3.
.phi.1, .phi.2 and .phi.3 having the same pulse width as .phi.4,
and have a pulse period which is three times as long as the period
of .phi.4.
In this method, the color filters 106 are arranged in stripes in
the Y direction and the frequency for changing over the color
signals can be delayed. Thus, the number of lines in the Y
direction can be made greater, a superior display resolving power
is obtained and a good quality color picture image is
reproduced.
FIG. 11 illustrates an exemplary embodiment of filter arrangement
and driving method of a color liquid crystal display in accordance
with the invention using the same point-at-a-time method used in
FIG. 10. However, the filters 116 are arranged in stripes in the X
direction. Thereby, the number of lines in the transverse direction
can be made greater and dots become similar to regular squares so
that a natural picture image can be produced.
The output of a shift register 112 selects driving electrodes 115
successively in synchronism with signals Yl through Ym. While one
of the driving electrodes 115 is selected, a shift register 111
selects successively a unit group comprising red, green and blue
filters. Additionally, red, green or blue (R, G, or B) selecting
clock signals .phi.1, .phi.2 or .phi.3 are signals formed by
dividing a clock signal .phi.5 into three phases. The color video
signals VSR, VSG and VSB are selected successively in synchronism
with these clock signals .phi.1, .phi.2, and .phi.3, and are
transmitted to the X driving line. In this method, the video signal
lines are in parallel with each other according to every color
video signal and connected to a sample hold switch 113. Thus, it is
advantageous that power consumption of the shift register 111 can
be reduced and the shift register is used within a range of its
operating speed because the frequency of the transmitting clock
.phi.5 of the shift register 111 is one-third of the number of
dots.
FIG. 12 illustrates an exemplary filter arrangement and driving
method of a color liquid crystal display in accordance with the
invention wherein respective colors R, G, and B of the color
filters are arranged in a mosaic pattern. Each color R, G or B is
allocated to a picture element and R, G and B are shifted by one
pitch distance to the left in order to bring about a left-down
pattern. For example, each picture element (FIG. 12) is driven by
signals from X and Y lines constructed on a glass plate as shown in
FIGS. 4-8. A shift register 122 for gate lines Yl . . . Ym outputs
signals for selecting lines Yl through Ym successively in
synchronism with a clock signal YCL. On the other hand, during a
period of selecting one line of the gate lines Yl . . . Ym, a shift
register 121 for data lines Xl . . . Xn outputs signals Sl through
Sn successively to the gates of transistors 123. Then, signals Vs
from an amplifier 124 are sampled successively and held on the
lines Xl through Xn by actuating the gates of the transistors
123.
Therefore, video signals are transmitted to respective picture
elements and a picture image is produced. In the video signal Vs,
the respective color signals VSR, VSB and VSG are lmultiplexed in
synchronism with clocks .phi.1 through .phi.3. Thus, it is
necessary that the timing of these clocks .phi.1 through .phi.3
correspond with the arrangement of each color filter allocated to
the picture element. For instance, during the period of selecting
the line Yl, a signal Sl must be applied to the transistor gate in
synchronism with the clock signal .phi.1.
That is, the row corresponding to Yl begins with a red filter. On
the other hand, during the period of selecting the line Y2, the
color signal must be applied to the transistor gate in synchronism
with the clock .phi.2 so that the row Y2 begins with a green signal
applied to a green filter. In other words, a video signal VSR must
be applied to a picture element R and video signal VSG must be
applied to a picture element G, and similarly with respect to the
blue signals and filters.
FIG. 13 shows signal waveforms associated with the configuration
and operation of the display device in accordance with the
invention of FIG. 12. When selecting the line Y1, a signal VSR is
first supplied to the line Xl in synchronism with the clock signal
.phi.1, while at the same time a sample-hold control signal S1 is
applied to the gate of the transistor 123 on the line X1. Second, a
color signal VSG is supplied to the line X2 in synchronism with the
clock signal .phi.2 during the period of the samplehold signal S2.
Third, a color signal VSB is supplied to the line X3 during the
period of applying the sample-hold signal S3.
When, for example, selecting the line Y2, first, the signal VSG,
second a signal VSB, third, a signal VSR are supplied to driving
electrodes via the lines X1, X2 and X3, respectively, in accordance
with the period of supplying the sample-hold controlling signals
S1, S2, and S3 to the gates of the transistors 123 on the lines X1,
X2 and X3. Thus, it is necessary to shift the clock signals .phi.1,
.phi.2, and .phi.3 going from one Y line to the next Y line in
order to supply one of the three primary color signals to each
driving electrode in correspondence with the three primary color
filters arranged in the mosaic pattern.
FIG. 14 illustrates a particular circuit for shifting the phases of
the clock signals .phi.1 through .phi.3. The circuit of FIG. 14
operates as indicated by the waveforms of FIG. 15. A 1/3 frequency
divider 143 is reset by a vertical synchronizing signal V and
outputs signals Q1 and Q2 to a 1/3 frequency divider 142 in
synchronism with a clock signal YCL. The 1/3 frequency divider 142
divides the inputted signals Q1 and Q2 into 1/3 in synchronism with
an X line clock signal XCL, and loads, that is, presets, the values
of Q1 and Q2 every time the horizontal synchronizing signal H is
inputted. Therefore, the phases of the outputs Q3 and Q4, applied
to decoder 141, are shifted for each clock pulse of the signal YCL.
Decoder 141 generates clock signals .phi.1 through .phi.3 with
proper timing in response to Q3 and Q4. Thus, and respective color
video signals are properly applied to the respective picture
elements R, G, and B in the circuit of FIG. 12.
FIG. 16 illustrates another exemplary embodiment of a color liquid
crystal device in accordance with the invention wherein filters are
arranged in a mosaic pattern. A red filter 161, green filter 162,
blue filter 163 and white filter 164 are formed as one block, and a
plurality of these blocks are arranged in a matrix. In the
situation of low level of light transmission through 3 color
filters, there is the problem of getting a poor reproduction of
white. In order to solve this problem, a transparent portion 164 is
added as a white filter and controlled by an illuminance video
signal VSW. Thus, the overall brightness can be improved and a
white color is well reproduced.
In this driving method, with regard to the X direction, a shift
register controls one block unit of four color filters in the same
manner as the circuit of FIG. 11 controls three filters.
Additionally, with regard to the Y direction, a gate line Yi or
Yi+1 is selected in synchronism with a clock signal .phi.. The
video signals VSR and VSB, or video signals VSG and VSW are
alternately applied to picture elements corresonding to each color
filter in synchronism with clock signals .phi.1 and .phi.2 which
have a frequency which is one-half of a clock signal .phi.3.
With regard to gray scale display techniques, FIGS. 17a, b indicate
how to control voltage amplitude in detail which is described
above. The video signal VS illustrated in FIG. 17a is sampled and
held in synchronism with a clock signal .phi.5 and is applied to an
X line. The characteristic curve of contrast in relation to applied
voltage V has an inclination as indicated in FIG. 17b. Thus, gray
scale reproduction can be displayed within the range of .DELTA.V.
Additionally, a better quality gray scale reproduction is achieved
by implementing .gamma. correction or video signal correction in
accordance with the characteristics of the liquid crystal
material.
The above means of gray scale reproduction through controlling
voltage amplitude is mainly adapted to drive an active matrix
composed of thin film transistors or non-linear elements, whereas,
another technique of gray scale reproduction, that is, controlling
or modulating pulse width, is primarily adapted to drive a matrix
of high duty cycle multiplex construction, or composed with
non-linear elements.
FIG. 18 illustrates an exemplary construction of a color picture
image display panel in accordance with the invention which is
driven by a pulse width modulation technique, operating as
indicated by the waveforms of FIG. 19. The color filters 186 are
arranged as a mosaic with a right-down pattern. For example, in a
duty cycle ratio multiplex technique, the driving electrodes are
arranged in the manner similar to FIG. 9c. Namely, the X-lines are
on the lower baseplate; the Y-lines are on the upper glass
baseplate, and the color filters are deposited on either side of
the X and Y electrodes.
The respective color video signals VSR, VSG and VSB are multiplexed
in synchronism with clock signals .phi.1 to .phi.3 in a manner as
discussed with reference to FIG. 12 and are applied to an
analog/digital converter 187 of four bits. The converted outputs
D.sub.0 through D.sub.3 are transmitted to a shift register 180
during the period of selecting a gate line Y, and the converted
outputs are supplied to a latch 181 in synchronism with a pulse
signal LP. A four-channel multiplexer 182 forms pulses having
different pulse widths, where four bits of data select one of
several time bases TB0 through TB3. These pulses are supplied to
the X-lines Xl to through Xn by way of a driver 183.
On the other hand, on the Y side, the gate lines are selected
successively by a shift register 184 and a driver 185 applies the
selecting signal to the Y driving electrodes.
With reference to FIG. 19, a frame has a positive field A and a
negative field B. The width of the driving pulse Xi is selected
within one selection period T SEL. For instance, when the gray
scale is zero, the driving waveform is shown as Xi (O). When the
gray scale is 7, the driving waveform is shown Xi (7), and when the
gray scale is 15, the driving waveform is shown as Xi (15). These
driving waveforms are formed by combining times bases TBO through
TB3 as indicated by the four-bit data signal.
In a high duty cycle multiplex method of a matrix driving method
utilizing non-linear element, the lines on the Y-side are formed by
dividing the driving electrodes into respective lines.
On the other hand, in a matrix driving method utilizing a thin film
transistor (TFT), a Y selection line is formed on the same base
substrate as the X side, and thus, in the liquid crystal driving
electrodes on the opposite substrate, a transparent driving
electrode film such as ITO (indium-tin-oxide), or a transparent
conductive film is deposited all over the surface of the opposite
substrate. Thus, when a TFT panel is formed as illustrated in FIG.
9, the transparent driving electrode film covers the color filter
entirely. Accordingly, this construction removes a problem that the
dyed layer in the color filter and the liquid crystal layer
interact with the each other and the reliability of both layers is
reduced. The construction where the transparent driving electrode
film entirely covers the color filters eliminates this problem
because the transparent electrode film shields the dyed layer from
the liquid crystal layer. This is a great advantage for a TFT panel
in that the transparent electrode film serves as a passivation film
for the color filter layers.
In a practical color display, a major problem sometimes occurs with
regard to resolving power. The methods of arranging color filters
in a mosaic pattern and for improving the resolving power are now
described. FIG. 20 illustrates a fundamental concept showing an
arrangement of picture elements in accordance with the invention.
FIG. 20a illustrates a technique wherein the color filters are
arranged by being shifted in adjacent rows by 1/2 of the pitch
distance between filters in the X direction. FIG. 20b shows a
technique wherein the color filters are shifted by 1/2 of the pitch
distance in the Y direction. The resolving power of the described
arrangements of picture elements is improved for viewing in an
oblique direction. Therefore, even with a monochromatic display, or
a graphic display, oblique lines do not appear unnaturally.
Favorable visual resolving power can be substantially obtained with
this arrangement where very few picture elements are used.
Additionally, in a multi-color display, the color filters R, G and
B are arranged repeatedly as positioned at each apex of a triangle
on a plane. Thus, a properly satisfactory resolving power is
obtained by this arrangement where few picture elements are
used.
FIG. 21 illustrates a construction of driving electrodes in a
multiplex driving system in accordance with the invention. X
electrodes 319 are arranged and shifted by 1/2 pitch distance for a
pattern as shown in FIG. 20a. The X and Y electrodes are normally
composed as transparent conductive electrodes, and sometimes,
wiring materials of very small width, which are made of a metallic
thin film, are deposited so as to lower the wiring resistance, if
necessary.
FIG. 22a shows an arrangement of filters and electrodes for
improving resolving power by utilizing TFT in accordance with the
invention. The arrangement includes data lines 213-215 and gates
lines 210-212. A transistor and a picture element electrode are
conventionally arranged for the odd numbered, that is, every other
gate line as shown with the transistor 216 and the picture element
electrode 217. On the other hand, in the even numbered gate lines,
transistors 219 and 222, and picture element electrodes 221 and 223
are arranged in parallel with each other on opposite sides of the
data line 214. In other words, there is substantially a 1/2 pitch
distance shifting. This example of FIG. 22a illustrates a case
wherein the data lines 213-215 and the driving electrodes 217, 220,
221 and 223 are formed in the same layer, or on the same layer. In
a construction where the data line and the driving electrode may
overlap, it is also possible to shift the picture element electrode
224 itself by 1/2 pitch distance with a single transistor 225 as
illustrated in FIG. 22b.
FIG. 23 shows another alternative embodiment wherein TFT is
utilized in accordance with the invention. Therein, shifting of the
data lines 230-232 by 1/2 pitch is achieved by making the lines
themselves zig-zag. It is advantageous in that the unnaturalness
caused by shifting electrodes by 1/2 pitch distance is removed,
because the size of the picture element is substantially the same
in both shifted portions and non-shifted portions.
FIG. 24 illustrates a technique of shifting the driving electrodes
by 1/2 pitch distance in the Y direction by making the gate lines
with a zig-zag pattern.
FIG. 25 is another alternative embodiment of a liquid crystal
device in accordance with the invention wherein TFT are utilized.
Drivers 270-273 are directly connected to data lines 277, 279, 281
and 283. The data lines 278, 280, 282 are alternately connected to
the right hand or the left-hand driver with every scanning of one
gate line. For instance, when the TFT are turned on by the gate
line 284 and the switches 274-276 are set to the left, the same
data is supplied to both picture elements 289 and 290, and 291 and
292 as pairs, respectively. Then, when the TFT are turned off by
the gate line 284 and are turned on by the gate line 285, the
switches 274-276 are set to the right, the same data is
respectively supplied to both elements of three pairs of picture
elements 294, 295, 296 and 297 and 298 and 299. Thus, a mosaic
similar to that shown in FIG. 20a is achieved.
FIG. 26 illustrates a mosaic construction as in FIG. 20a, wherein
the X data lines 311, 312, 313 are wired in a zig-zag pattern.
As stated above, a color display in accordance with the invention,
can be achieved by combining a color filter with a driving method
for a large number of dots such as a high duty cycle ratio method,
a multiplex driving method, or a driving method wherein a thin film
device, such as a non-linear element or a thin film transistor, is
utilized, and the like. A light transmission type display can be
utilized when power consumption is not severely limited. A light
reflection type display wherein a plane of reflection is deposited
on the lower side can be utilized where low power consumption is
required. A color display in accordance with the invention is
advantageous as compared with cathode ray tube of the same quality
picture in that a full color display composed of more than
100.times.100 lines can be achieved with excellent image quality
and without distortion, with a compact physical unit and low power
consumption in reproducing graphic or picture images.
It will thus be seen that the objects set forth above, among those
made apparent from the preceding description, are efficiently
attained and, since certain changes may be made in the above
construction without departing from the spirit and scope of the
invention, it is intended that all matter contained in the above
description or shown in the accompanying drawings shall be
interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended
to cover all of the generic and specific features of the invention
herein described, and all statements of the scope of the invention
which, as a matter of language, might be said to fall
therebetween.
* * * * *